Dampening Field grants you advantage, it does not remove disadvantage
The feature states:
You have advantage on Dexterity (Stealth) checks. If the armor normally imposes disadvantage on such checks, the advantage and disadvantage cancel each other, as normal.
This is explicitly addressed when the feature says "If the armor normally imposes disadvantage on such checks, the advantage and disadvantage cancel each other, as normal" but I will explain it further:
If you would be making a regular roll, you now make one with advantage instead, and if you would be making a roll with disadvantage, you now make a regular one instead.
Dampening Field grants you advantage and does not actually remove disadvantage like a few other features do, for example, the Drunken Master Monk's Drunkard's Luck feature, which states:
When you make an ability check, attack roll, or a saving throw and have disadvantage on the roll, you can spend 2 ki points to cancel the disadvantage for that roll.
This feature is worded such that it actually cancels disadvantage whereas Dampening Field is worded such that it adds advantage.
Note that having advantage from multiple sources will not change this because the rules on "Advantage and Disadvantage" state:
If circumstances cause a roll to have both advantage and disadvantage, you are considered to have neither of them, and you roll one d20. This is true even if multiple circumstances impose disadvantage and only one grants advantage or vice versa. In such a situation, you have neither advantage nor disadvantage.